On 1/21/22 12:42 AM, Pasha Tatashin wrote:
> The pte entry that is used in pte_advanced_tests() is never removed from
> the page table at the end of the test.
>
> The issue is detected by page_table_check, to repro compile kernel with
> the following configs:
>
> CONFIG_DEBUG_VM_PGTABLE=y
> CONFIG_PAGE_TABLE_CHECK=y
> CONFIG_PAGE_TABLE_CHECK_ENFORCED=y
Assuming this is on latest mainline.
I could enable PAGE_TABLE_CHECK on arm64 after some hacks. It did not build
on the platform otherwise. But enabling DEBUG_VM_PGTABLE afterwards did not
create below mentioned problems. Is the problem x86 specific ?
>
> During the boot the following BUG is printed:
>
> [ 7.483050][ T1] debug_vm_pgtable: [debug_vm_pgtable ]:
> Validating architecture page tabs
> [ 7.490930][ T1] ------------[ cut here ]------------
> [ 7.494926][ T1] kernel BUG at mm/page_table_check.c:194!
Which BUG() is this ? mm/page_table_check.c:194 on latest mainline ..
void __page_table_check_pud_clear(struct mm_struct *mm, unsigned long addr,
pud_t pud) <----
> [ 7.499172][ T1] invalid opcode: 0000 [#1] PREEMPT SMP KASAN
> [ 7.503610][ T1] CPU: 0 PID: 1 Comm: swapper/0 Not tainted 5.16.0+
> [ 7.508600][ T1] Hardware name: QEMU Standard PC (i440FX + PIIX,
> ...
>
> The entry should be properly removed from the page table before the page
> is released to the free list.
>
> Fixes: a5c3b9ffb0f4 ("mm/debug_vm_pgtable: add tests validating advanced arch page table helpers")
I am not sure whether this really fixes an existing problem.
>
> Signed-off-by: Pasha Tatashin <pasha.tatashin@xxxxxxxxxx>
> Reviewed-by: Zi Yan <ziy@xxxxxxxxxx>
> Tested-by: Zi Yan <ziy@xxxxxxxxxx>
> ---
> mm/debug_vm_pgtable.c | 2 ++
> 1 file changed, 2 insertions(+)
>
> diff --git a/mm/debug_vm_pgtable.c b/mm/debug_vm_pgtable.c
> index a7ac97c76762..db2abd9e415b 100644
> --- a/mm/debug_vm_pgtable.c
> +++ b/mm/debug_vm_pgtable.c
> @@ -171,6 +171,8 @@ static void __init pte_advanced_tests(struct pgtable_debug_args *args)
> ptep_test_and_clear_young(args->vma, args->vaddr, args->ptep);
> pte = ptep_get(args->ptep);
> WARN_ON(pte_young(pte));
> +
> + ptep_get_and_clear_full(args->mm, args->vaddr, args->ptep, 1);
> }
Although I dont see any problem on arm64 after this change.
>
> static void __init pte_savedwrite_tests(struct pgtable_debug_args *args)
>
